LCMO layered Noise Studies of Disordered Condensed Matter M. B. Weissman, UIUC, DMR Colossal Magnetoresistive (CMR) materials have inspired interest for their potential as sensors of magnetic fields, most evident in a regime where a magnetic conducting phase and a non-magnetic insulating phase coexist. Two main factors- disordered atomic positions in solid solutions and strain interactions between different regions- have been proposed as the keys to the phase- coexistence regime. Using noise to identify the phase coexistence regime, we have shown that in films it is scarcely changed by replacing the solid solution with an ordered layered material, indicating that the strain interactions are a key factor. LCMO Solid solution The layered sample has a slightly wider phase coexistence range (double-headed arrow) than the disordered sample, indicating that disorder plays a smaller role than strain interactions.

The sensitivity of most CMR materials to magnetic fields comes mainly from the mixture of electrically conducting and electrically insulating regions. Applying a magnetic field makes the conducting regions, which are magnetic, grow. Most simple theories, however, do not predict that such mixed-phase states would be stable. Are they stabilized in the way water-ice mixtures are stabilized if put in a fixed-volume bottle? Or is the stability mainly due to the variation in properties from site to site caused by the disordered locations of the atoms? We find here that changing from the standard disordered material to an unusual one with ordered layers causes little change in the phase coexistence. We believe the main physical cause resembles that for water-ice in a bottle.

Education: This grant supports work by four graduate students (Andrea Mills, Lambert Chao, Aki Palanisami, and David Layton) as well as a Visiting Research Professor (Eugene Colla). Recent graduates from this group have gone on to work for several hard-drive developers, as well as for other hardware developers, national labs, and universities. The work described in this nugget was done by Palanisami in collaboration with Mathur’s group from Cambridge University and with Eckstein’s group at Illinois. Outreach: The PI has prepared and edited many dozens of answers for a question-and-answer Web site run by the Physics Department site This site draws questions on all sorts of science topics from students of all ages from around the world. Here’s the PI’s favorite: bout_space/the_earth_and_the_moon/ htm. Here’s another, with more serious substance: _of_matter_and_energy/boiling_evaporating_ and_condensing/ htm. Noise Studies of Disordered Condensed Matter M. B. Weissman, UIUC, DMR